1. Field of the Invention
The present invention relates to an inkjet printing apparatus and an inkjet printing method. More particularly, the present invention relates to an inkjet printing apparatus and an inkjet printing method, for performing printing while causing a printing head which ejects different kinds of inks to scan back and forth on a printing medium.
2. Description of the Related Art
A serial inkjet printing apparatus is widely used since it is easy to realize miniaturization thereof with a relatively inexpensive configuration. In this printing apparatus, print scanning of a printing head and transfer of printing medium are repeated to sequentially form images on the printing medium.
FIG. 2 is a perspective view for explaining a schematic configuration of a serial inkjet printing apparatus. Reference numeral 22 denotes a printing head, which is formed of six printing heads 22K, 22LC, 22C, 22LM, 22M and 22Y for ejecting six colors of inks. The printing heads 22K, 22LC, 22C, 22LM, 22M and 22Y eject the respective colors of inks, including black (K), light cyan (LC), cyan (C), light magenta (LM), magenta (M) and yellow (Y). The printing heads of the six colors are aligned in parallel in a main scanning direction (direction B) in FIG. 2.
Before printing is started, the printing head 22 is set at a position (home position) shown in FIG. 2. Upon receipt of a command to start printing, the printing head 22 performs printing on a printing medium 1 by a width corresponding to an arrangement range of ejection ports of the printing head 22 while moving (scanning) in a direction indicated by the arrow B (forward scanning direction). By this one time of scanning, a band-like image region (band) as shown in FIG. 15 is formed. In this scanning in the forward scanning direction (forward scanning), the six colors of inks are applied onto the printing medium 1 in the order of black, light cyan, cyan, light magenta, magenta and yellow. Thereafter, when printing for this one scanning (for one band) is finished, the printing head carries out printing for another band by applying the inks while moving in the direction indicated by the arrow B (backward scanning direction) toward the home position. In this backward scanning, the inks are applied onto the printing medium in the order of yellow, magenta, light magenta, cyan, light cyan and black, which is opposite to that in the forward scanning. Between the end of one print scanning and the start of the next print scanning, transfer rollers 3 are rotated to transfer the printing medium 1 for a predetermined amount in a direction indicated by the arrow A. The print scanning for one band and the predetermined amount of transfer operation as described above are repeated to form a desired image on the printing medium 1.
Meanwhile, much faster printing has recently been demanded as means for increasing work efficiency of a printer user. Therefore, in order to respond to the demand, bidirectional printing is more and more often adopted also in the serial inkjet printing apparatus. However, since a water-based liquid ink is used in many inkjet printing apparatus, a certain amount of fixing period is required before the ink is dried after being applied onto a printing medium. If, before the ink is completely dried, the printing medium is placed on another printing medium or a printing surface thereof is rubbed, the printing medium is smudged. Thus, a so-called smear problem occurs.
Particularly, in the case of double side printing in which printing is performed on both sides of a printing medium, the problem becomes more complicated. Generally, in the double side printing, the printing medium printed on its front surface is inversed by inversion mechanism. However, if the printing medium printed on its front surface is inversed, ink applied on the surface is contact with the parts of the inversion mechanism or the transferring pathway, and the parts of the inversion mechanism or the transferring pathway are messed. Particularly, the transferring roller in the inversion mechanism (hereinafter referred to as inversing roller) is attached much contamination, moreover the contamination of the inversing roller is retransferred onto another printing medium, the smear problem occurs.
To solve the problem as described above, for example, there is also conceivable a method for providing means for facilitating drying of the printing medium immediately after printing by installing a heater in the printer. However, by use of such a method, the heater or a new structure has to be provided. Thus, the printer may become large in scale and expensive. Particularly, as to a small inkjet printing apparatus which has become popular among personal users, application thereof is in a difficult situation from the viewpoint of power consumption, heat insulation and safety.
Therefore, in the inkjet printing apparatus having concerns over the smear problem and the transfer problem in the double side printing, time for drying ink is generally provided during page printing or before paper discharging (or paper refeeding) (see, for example, U.S. Pat. No. 6,149,327). The time for drying the ink may be automatically set or may be set by a user on a printer driver in a host device or on a main body of the printer. In the latter case, the user selects the time for drying from set values prepared for several stages such as “none (=waiting for 0 second)”, “normal (=waiting for 5 seconds)”, “long (=waiting for 10 seconds)” and “longer (=waiting for 20 seconds)”. Alternatively, the user inputs the drying time by the second himself/herself.
Meanwhile, in recent years, in order to harmonize both of black character quality and color picture image quality, there have also been provided a number of inkjet printing apparatus having black ink and color ink, which have different properties in permeation, diffusion and the like. For example, there has also been proposed a printer which uses a pigment as a color material of the black ink and uses dyes as the color ink. Moreover, in order to enhance image quality after printing, there has also been provided an inkjet printing apparatus including a liquid which reacts with ink or including a plurality of inks which react with each other (see, for example, Japanese Patent Application Laid-open No. 2004-106296). In this case, ambiguity (e.g., feathering) at the edges of black characters and color bleeding are prevented, as is excessive permeation of printing medium by ink. As a result, a high quality, high density images can be obtained.
In the case where bidirectional printing is carried out by installing a large variety of inks (or liquids) having properties different from one another as described above in the serial inkjet printing apparatus as described in FIG. 2, an ink application order in the forward scanning is different from an ink application order in the backward scanning. According to the study done by the inventors of the present invention, it is confirmed that, in the above-described case, there emerges a difference in fixing properties between an image printed in the forward scanning and an image printed in the backward scanning.
However, in the conventional inkjet printing apparatus, the drying time described above is not set by taking account of a difference in ink fixing properties in the bidirectional printing. Basically, the drying time enough to prevent the smear problem and the transfer problem is set by comparing fixing period between the image formed in the forward scanning and the image formed in the backward scanning, and thereby adopting the longer fixing period. In this case, needlessly long drying time makes it difficult to achieve an effect of the bidirectional printing which makes high-speed output possible. As to the printer, one of important challenges in recent years is how to prevent printing time from being prolonged while grasping the fixing period that changes according to situations, such as in the forward scanning and in the backward scanning, as accurately as possible and while setting proper drying period.